If you want children who are going to do well at school, have two of them. Those who have one younger brother or sister have better educational results than those in bigger or smaller families. Although some well known geniuses might appear to give the findings some credence, others overcome the odds (natural talent will out whatever the family position).
My wife wants two children and I've always said I wanted three, and since the next best performers were the middle of three, youngest of three and eldest of six, (the youngest of two is not mentioned) then my proposition seems to have a better end result, doesn't it? He he...